The present invention relates to an induction heat cooking apparatus in which a high frequency electromagnetic field is generated by a heating coil, and the generated electromagnetic field is supplied to a load so that the load is inductively heated.
In a conventional induction heat cooking apparatus, a temperature sensor is mounted at the rear surface (heating coil side) of a top plate on which a load or vessel is placed. The vessel temperature measured by the temperature sensor is compared with a set temperature. The set temperature is preset by a temperature set portion located at a manipulation part of the cooking apparatus. When the vessel temperature comes close to the set temperature, the heating power is decreased. Further, if the vessel temperature exceeds the set temperature, heating is stopped or any other proper process is performed so that the vessel is kept at a suitable temperature around the set temperature.
According to the above conventional cooking apparatus, however, the cooking apparatus operator cannot determine whether or not the vessel is really kept at a desired or optimum temperature. Because of this, regardless of the above vessel temperature control function, the resultant cooked food could be untasty. For instance, when fried food is cooked, even if the oil temperature in a vessel is optimum, putting in the frying material renders the oil temperature lower, thereby impairing the quality of the resultant fried food.
Further, in a conventional induction heat cooking apparatus, if heating is carried out without use of a standard vessel or if heating is carried out by using a strange vessel whose material and/or size are not standard the heating coil is subjected to excessive overcurrent, resulting in damage to the heating coil as well as other associated materials. To prevent such damage, in a conventional induction heat cooking apparatus, whether or not a standard vessel is properly used is detected, and the detected result is indicated. If a standard vessel is not properly set, the excitation of the heating coil is inhibited.
One method for judging whether or not a standard vessel is properly set utilizes magnetism. According to this method, however, even though a vessel with a magnetic substance can be detected, a nonmagnetic heatable vessel such as an 18-8 stainless steel vessel cannot be detected.
Another method for judging whether or not a standard vessel is properly set detects a voltage and current of a temporarily excited heating coil at the time when the heating starts, or it detects a voltage and current of an excited heating coil during the heating. According to this method, it is possible to detect not only a magnetic vessel but also a nonmagnetic 18-8 stainless steel vessel.
In recent years, an induction heat cooking apparatus having a temperature adjusting function has been developed for the purpose of convenience. Such a cooking apparatus is provided with a temperature sensor portion for measuring the temperature of a vessel and a temperature set portion for presetting the vessel temperature. In such a cooking apparatus, heating is effected when the vessel temperature is lower than the set temperature, and heating is interrupted when the vessel temperature exceeds the set temperature. Then, the vessel temperature is roughly maintained around the set temperature. However, when a load detecting function based on the detection of a voltage and current is adapted to the above induction heat cooking apparatus, a disadvantage could develop. That is, since the load detecting function is disenabled under the interruption of heating, if a standard vessel is replaced with a nonstandard vessel at the time of the interruption, no indication for such an improper replacement is indicated. Such a situation discredits the cooking apparatus in the eyes of the operator.